Hitherto, a variety of hydrogen occluding alloys have been suggested, as exemplified by a hydrogen occluding alloy disclosed recently in "INTERNATIONAL SYMPOSIUM REGARDING THE FOUNDATION AND APPLICATION OF METAL-HYDROGEN SYSTEMS", held on Nov. 6 to 11, 1994, in Fujiyoshida, Japan.
The foregoing hydrogen occluding alloy is a Ni--Zr based alloy having a composition according to the formula: EQU Ti.sub.0.5-x/2 Zr.sub.0.5-x/2 La.sub.x Mn.sub.0.8 Cr.sub.0.8 Ni.sub.0.4, in which x=0.0-0.1.
Such alloys have a two-phase structure comprising a main phase made of a Zr--Ni--Mn based alloy and a phase made of a La--Ni type alloy which is dispersively distributed along the grain boundary of the main phase, as illustrated in an enlarged schematic view of the structure in FIG. 3.
In the foregoing conventional hydrogen occluding alloy, the phase made of the La--Ni type alloy dissociates atmospheric hydrogen molecules (H.sub.2) to form hydrogen atoms (H) by its catalytic action, and absorbs the dissociated hydrogen atoms at a rate higher than that of the main phase made of the Zr--Ni--Mn based alloy; thus the absorption of the hydrogen atoms in the main phase made of the Zr--Ni--Mn based alloy is carried out mainly through the phase made of the La--Ni type alloy; and the hydrogen desorption is carried out by a function contrary to the foregoing function.
In addition, the foregoing conventional hydrogen occluding alloy can be made by preparing a Ni--Zr based liquid alloy having the foregoing composition, casting it into an ingot, and annealing the ingot for homogenization at a predetermined temperature within the range from 950 to 1,050.degree. C. for a predetermined time in a nonoxidizing atmosphere, such as vacuum or inert gas.
In general, when the hydrogen occluding alloy is applied to an electrode of a battery, the battery can serve a practical use after an initial activation treatment in which charge/discharge cycles are repeated until the electrode including the hydrogen occluding alloy has a sufficient discharge capacity, in other words, until the discharge capacity caused by the hydrogen occluding alloy reaches near its maximum.